FIG. 1 depicts a diagram of the salient components of wireless telecommunications system 100 in accordance with the prior art. Wireless telecommunications system 100 comprises: mobile station 101, wireless base stations 102-1, 102-2, and 102-3, wireless switching center 111, assistance server 112, and location client 113. Wireless telecommunications system 100 provides wireless telecommunications service to all of geographic region 120, in well-known fashion.
The salient advantage of wireless telecommunications over wireline telecommunications is the mobility that is afforded to the user of the mobile station. On the other hand, the salient disadvantage of wireless telecommunications lies in that fact that because the mobile station is mobile, an interested party might not be able to readily ascertain the location of the mobile station.
Such interested parties might include both the user of the mobile station and remote parties. There are a variety of reasons why the user of a mobile station might be interested in knowing his or her location. For example, the user might be interested in telling a remote party where he or she is or the user might seek advice in navigation.
In addition, there are a variety of reasons why a remote party might be interested in knowing the location of the user. For example, the recipient of an emergency call (e.g., E-911) from a user might be interested in knowing the location of the mobile station so that emergency services vehicles can be dispatched to the user.
There are many techniques in the prior art for estimating the location of a mobile station. The common theme to these techniques is that location of the mobile station is estimated based on the electromagnetic (e.g., radio, etc.) signals—in one form or another—that are processed (i.e., transmitted or received) by the mobile station.
In accordance with one family of techniques, the location of a mobile station is estimated based on the transmission range of the base stations with which it is communicating. Because the range of a base station is known to be N meters, this family of techniques provides an estimate for the location that is generally accurate to within N meters. A common name for this family of techniques is “cell identification” or “cell ID.” The principal disadvantage of the family of cell ID techniques is that there are many applications for which the accuracy of the estimate for the location it generates is insufficient.
In accordance with a second family of techniques, the location of a mobile station is estimated by analyzing the angle of arrival or time of arrival of the signals transmitted by the mobile station. A common, if somewhat inaccurate, name for this family of techniques is called “triangulation.” The principal disadvantage of the triangulation techniques is that there are many applications for which the accuracy of the estimate for the location it generates is insufficient.
In accordance with a third family of techniques, the location of a mobile station is estimated by a receiver in the mobile station that receives signals from satellites in orbit. A common name for this family of techniques is “GPS.” The principal advantage of the GPS techniques is that when it works, the estimate for the location can be accurate to within meters. The GPS techniques are disadvantageous in that they do not work consistently well indoors, in heavily-wooded forests, or in urban canyons.
In accordance with a fourth family of techniques, the location of a mobile station is estimated by pattern matching one or more location-dependent traits of one or more electromagnetic signals that are processed (i.e., transmitted and/or received) by the mobile station. Common names for this family of techniques include “Wireless Location Signatures,” “RF Pattern Matching,” and “RF Fingerprinting.”
The basic idea is that some traits of an electromagnetic signal remain (more or less) constant as a signal travels from a transmitter to a receiver (e.g., frequency, etc.) and some traits change (e.g., signal strength, relative multi-path component magnitude, propagation delay, etc.). A trait that changes is considered a “location-dependent” trait. Each location can be described or associated with a profile of one or more location-dependent traits of one or more electromagnetic signals. A mobile station at an unknown location can observe the traits and then attempt to ascertain its location by comparing the observed traits with a database that correlates locations with expected or predicted traits.
There are various modifications that can be made to the basic Wireless Location Signatures technique to improve the accuracy of the estimate for the location. The principal advantage of the Wireless Location Signatures technique is that it is highly accurate and works well indoors, in heavily wooded forests, and in urban canyons.
At least some of these techniques are sufficiently accurate to satisfy the requirements of current public safety applications such as E-911. There are, however, other applications for which these techniques are not sufficiently accurate to satisfy the requirements thereof. For example, some law enforcement applications might require the capability to determine a particular hotel room in which a kidnapper is hiding with a victim. Similarly, a person might need to be located to within a specific apartment, vehicle, or seat in a stadium or venue.
What is needed is a technique that provides a higher level of accuracy of location estimation for certain applications than what is achievable with at least some techniques in the prior art.